Oh hell yes, using them for fighters is super fun, because while
8byte mentions you can only use them for single button inputs, you can use it creatively to make certain combos easier to preform without having to use a crazy claw grip.
One example is in Garou. There is a special version of terry's power dunk that lets you cancel it if you press a shoulder button almost a couple frames after you do the motion with a face button.
Timing the input with my thumb and pointer was a pain in the ass without reconfiguring controls and then you would have to relearn your moves. With these back buttons I putt the button I need to hit to cancel on the right bumper and I can activate it faster than pressing l1 or r1 and can do it flawlessly now.
Honestly think they might be banned because I can see this allowing for some links that were very strict to be easy now.